1. Field of the Invention
This invention relates to a lens drive arrangement for an automatic focusing device.
2. Description of the Prior Art
In situations where an automatic focusing device is required to perform a continuous focusing operation, a servo-like control using a motor or the like is employed as a typical lens driving method. In conventional automatic focusing devices, however, there is the probability of erroneous detection during a lens position adjusting process and such a probability increases particularly where the lens position is shifted at a high speed or where sensors of low sensitivity are used. As a result, conventional devices of this type have been compelled to drive the lens at a very low speed. Accordingly, photographers have often missed good shutter chances. Furthermore, in the servo-like control, the motor is controlled by a servo system. Generally, however, there arises an overshoot problem during control by a servo system. When the lens is driven to an in-focus point, the lens does not stop there but is apt to move to a point beyond the in-focus point. Therefore, in shifting the lens to an in-focus position under servo-like control, hunting of the lens might occur. In such a situation, the lens slowly reaches the in-focus point after moving back and forth across the in-focus point. Under the servo-like control, the lens can be brought into an in-focus position once a lens driving direction toward the in-focus point is detected. However, where more speedy and more accurate automatic focusing is desired, it is preferable to promptly shift the lens position to an in-focus point by virtue of defocus degree information.